The present invention relates to a system for monitoring damage to a rotor blade of a rotary-wing aircraft, to an aircraft rotor blade and to an aircraft fitted with such a system.
The technical field of the invention is that of manufacturing rotary-wing aircraft.
Various devices for monitoring damage to a blade of a rotor for providing a helicopter with lift and forward drive have been proposed.
Patents FR 2 119 182 and U.S. Pat. No. 3,744,300 describe a device for measuring damage due to fatigue in a helicopter blade, the device including a sensor comprising strain gauges connected in a Wheatstone bridge configuration.
U.S. Pat. No. 4,106,332 describes a device for detecting an interruption in a conductive loop applied to the surface of a helicopter rotor blade; the device includes a bistable serving, in flight, to record a state corresponding to detecting a fault that led to the conductive loop being interrupted; when the aircraft is on the ground, a unit can be connected to the blade in order to read the state of the bistable in order to test the blade while it is at rest.
A drawback with such systems is that they do not make it possible to determine the location and the extent of the fault affecting the blade.
U.S. Pat. No. 3,596,269 describes a system for detecting and monitoring structural faults in the skin of an airplane. That system comprises a group of thin elongate electrical conductors constituted by two metal sheets interconnected by a resistor; the conductors are connected in parallel and they are placed between two insulating sheets; the assembly is stuck to different points on the skin of an airplane. A switch enables an operator manually to select a group for measuring its resistance by means of an ohmmeter; a visual or audible alarm is provided.
A drawback with such systems is that they are adapted poorly or not at all to monitoring the defects that might appear on the surface or inside a blade made of composite material.
U.S. Pat. No. 4,524,620 describes apparatus for acoustically monitoring the noise emitted by a composite helicopter blade; the blade is fitted with one or more acoustic transducers and the signals therefrom are multiplexed where necessary, and then filtered and forwarded to a computer or to a recorder; a filter serves to detect and eliminate “normal” noise so as to pass only “critical” noise representative of excessive stresses in the blade and structural damage caused to the blade; the occurrence and the intensity of such critical noise are accumulated in the recorder or the computer in order to constitute a history of critical noise from a given blade.
Such a device is complex; furthermore locating a defect in the blade requires triangulation calculations to be performed, in deferred time, and on the ground, using an auxiliary computer.